The present invention broadly relates to a new and improved apparatus for butt welding of hollow cylindrical and longitudinally or axially slit blanks to form wheel rim hoops.
Generally speaking, the apparatus for butt welding of hollow cylindrical and longitudinally or axially slit blanks to form wheel rim hoops comprises means for pressing together the mutually confronting edges of the longitudinal or axial slits of the hollow cylindrical blanks. Clamping devices or work locating fixtures are associated with each region of the hollow cylindrical blanks adjoining the axial slit and are used for fixedly clamping each region and for conducting an electrical current to each region. Each clamping device of the clamping devices comprises a first fixed clamping jaw and a second movable clamping jaw. There is provided a source of electrical welding current. The first fixed clamping jaw is connected to the source of electrical welding current. Each hollow cylindrical blank has an inner circumference and the second movable clamping jaw is intended to engage one hollow cylindrical blank at a time at the inner circumference. The second movable clamping jaw is movable toward and away from the first fixed clamping jaw.
Such an arrangement, for example, is known from U.S. Pat. No. 2,713,626, granted July 19, 1955.
In this prior art apparatus each of the two work locating fixtures possesses a movable clamping jaw which with its associated fixed clamping jaw forms a type of "alligator" mouth into which the blank is to be pushed in a direction parallel to its axis. The closing movement of the movable clamping jaw onto or toward its associated fixed clamping jaw is a pivotal movement with the result that the specific contact pressure is not necessarily always uniform over the whole clamping surface. Consequently the welding current has to overcome different transition resistances which can lead to unwanted local heating in the region of the welding joint to be fabricated. Since the blanks additionally have to be brought to the clamping jaws by means of an axial movement and again have to be removed from the clamping jaws by an opposite axial movement, the feeding and removal of the workpieces in the prior art apparatus is either possible only by hand or only with a considerable technical effort. If the prior art apparatus is to be rebuilt for automatic operation it would require a robot-type apparatus for the feed and removal of the blanks.
For the sake of completeness it should be mentioned that a similar arrangement is known from British Pat. No. 1,556,556 although from non-analogous art. The arrangement forms a station in a production line of a number of stations that are described in this British patent. Strips of metal, precut to an exact length, are fed to the first station and bent by bending rolls into longitudinally slit blanks. There extends through all stations of the production line a guide pin which is anchored at only one side of the first station and along which the blanks are axially driven, a step at a time, by rhythmically reciprocating grippers or grabs from station to station. The second station of the production line is a stamping station which in the present connection is only of interest insofar as the female dies associated with the male stamping or pressing dies or punches are anchored in the region of the stamping station on the aforementioned guide pin.
The third station is the welding station and, considered alone, corresponds to the aforementioned similar apparatus of U.S. Pat. No. 2,713,626. However, the fixed clamping jaws of this welding station are fixed to the guide pin and the movable clamping jaws act from the outer circumference on to the edge area bordering the longitudinal slit of the blank.